Question
Hydrogen bonds are formed in many compounds e.g., $${H_2}O,HF,N{H_3}.$$ The boiling point of such compounds depends to a large extent on the strength of hydrogen bond and the number of hydrogen bonds. The correct decreasing order of the boiling points of above compounds is
A.
$$HF > {H_2}O > N{H_3}$$
B.
$${H_2}O > HF > N{H_3}$$
C.
$$N{H_3} > HF > {H_2}O$$
D.
$$N{H_3} > {H_2}O > HF$$
Answer :
$${H_2}O > HF > N{H_3}$$
Solution :
Strength of hydrogen bonding depends on the size and electronegativity of the atom. Smaller the size of the atom, greater is the electronegativity and hence stronger is the $$H$$ - bonding. Thus, the order of strength of $$H$$ - bonding is $$H...F > H...O > H...N.$$ But each $$HF$$ molecule is linked only to two other $$HF$$ molecules while each $${H_2}O$$ molecule is linked to four other $${H_2}O$$ molecules through $$H$$ - bonding.
Hence, the decreasing order of boiling points is $${H_2}O > HF > N{H_3}.$$